Estimate erect penis size?

Last week I have had an interssting conversation with other guests of a party (boys and girls). One girl said that its easy to see if somebody is a grower or shower. Her argumentation was that the flaccid penis of a grower has a darker pigmentation than the flaccid penis of a shower. After some counterparts of other people she limited her statement for white guys only.
What do you think? Is it true or just a random observation of her?